Artificial leather



U TED] STAT this invention,

latented July 14, 1942 Es PAT ARTIFICIAL Lith um i.--' I Philip I. Robb ,Iiet'r it, Mithl, assignor a" Hercules Powder Company, Wilmington, Del., a

corporation of Delaware" g No Drawing.

Application November 26,1938, Q I Serial N0. 242,557 V i is Claims. (01. 117-166) I This invention relates to improved artificial leather andmore particularly'to artificial leather containing nitrocellulose 'and whichls capable of' retaining its flexibility at low temperatures;-

, and'of retaining its softener at high tempera- ,i ur q Y. I Y.

I Artificial leather consists-of a flexible base and fa pigmented coating of nitrocellulose softened chiefly by a vegetable oil, usually castor-coils:

Castor oil imparts an excellent resilience to the coating andis therefore generally used, However,

artificial leather utilizing it"has not been wholly satisfactory for some purposes, such as for autosuch-as, for example, oxidized caster oil, oxidized soy bean oil, oxidized cottonseed oil, and thelike.

Oxidation is; usually accompanied by polymerization andsince highly ,polymerizedzoils; impart low -.temperature brittleness to a coatin it islprefer- I able to utilize only ,such"oxidized oils as have I been-polymerized-to arelatively mild degree; By

\ the aforesaid term I- also includevegetable oils slightly polymerized by other means,,for example,

by heat, but itis to be'noted that oils; polymerized more than slightly byheat alone do not fit the "said term as they are incompatible with the celmobileupholstery, because of two related defects. I 3 One is that upon exposureto the sun in very hot I weather, the'heat'absorbed causes 'oil to exude from the'coating. q The second and more serious I defect is that "in very cold weather, the coating becomes brittle. The defect of exudation has high temperaturescould be prevented and-at the same ume-flexibility at low temperatures 'could be improved. To accomplish this is an object of Now', in accordance with my invention, the

' tendency of artificial leather coatings to exude softener upon being heated is ellminated'andat the same time the temperature at" which the I coating becomes embrittled upon being cooled is appreciably lowered. I-have further found in my inventiona way of improving the durability 3 of -the product. "Briefiystated. anartificial leather in ac 'cordance'with-my invention comprises a modl eratelyheavy web-like flexible base and thereon a I flexible coating comprising a mixtureofnitrocellulose with ethyl cellulose whichis soluble in the usual organic solvents and a vegetable oil softener compatible with the said cellulosic mix- I ture, Pigments orfillers. or both may be included i m: the coatings. Softener mixtures compatible with the said cellulosic mixture such .as a mixtureof a vegetable oil softener-with another softener may be utilized,

By the term',;a=vegetable oil soften'er compatible (withv the cellulosic mixture, I include raw vegetable oilssuch as, for .example, castor oil, soy

,lulosic mixture. "softener, I also include mixtures of the vegetable By the termyavegetable oil oils mentioned hereinabove; However, I prefer to utilize raw castor oil-or caster oil whichhas been ,slightlypolymerized byoxidation as the vegetable oil softener of this invention. I

The nitrocellulose utilized in the coating is one soluble in the usual artificial leather. solvents.

Preferably, it has a nitrogen content of about 11% to about 12.6%. Its viscosity is'preferably above that of the type known as RS 100 .Second Nitrocellulose but a useful artificial leather can be made with '15 second. nitrocellulose ,or lower I viscosity. nitrocellulose, although the toughness of the coating decreases as. viscosity is lowered. The ethyl cellulose which I utilizein the coating of my improved artificial leather is one' soluble in the usual organic solvents of the art, that is,

. .one with an ethoxy content in the range of about 341% to about 51%. Preferably the ethoxy content is in the range of about-44 to about. 48%.

,The viscosity, as in the case of the nitrocellulose,

is'preferably high so as to obtain maximum toughness. utilize an ethyl cellulose witha viscosity of about 60 to abouty80 seconds or above about 60 seconds, I as measured by the number of seconds reguired for satsteel ball to fall through 10 inchesof a 20% solution of the ethyl cellulose in a solvent consisting of 80 parts toluene and 20 parts ethyl alcohol, the solution being maintained at 25 C. in I a tube oneinch in inside diameter.

@The. moderately heavy web-like flexible base I .of my artificialleather is any one of the usual j cloth of sheeting, sateen, broken twill, etc. conartificialleather basessuch as a cotton or other struction, or such as a fibrous'felt ofsimilar thicknessor a latex impregnated felt,=and so forth. Such bases generally vary: in weight from I1 about .3 ounces to about l2 ounces per square I -yard."

bean oi1,-and the like, and oxidized vegetable oils 55 Theimproved artificial leather inaccordance with my invention may have,, for example, from It is. preferable,, for example, to-

about Bounces to about 14 ounces, say about 8 ounces, dry weight of the coating composition deposited per square yard of the flexible base.

This coating will comprise, for example, a mixbefore mentioned for a vegetable softener alone. The fiexible coating may include the fillers and pigments usual in artificial leather. Desirably, I utilize pigments high in covering power such as, for example, titanium dioxide, and especially pigments which are also highly opaque to ultraviolet light such as, for example, lead titanate and carbon black.

Thea'rtificial leather in accordance with this invention may be prepared by any of the common methods of the art. Conveniently, a coating dope is prepared by mixing an alcohol-wet nitrocellulose, ethyl cellulose, softener or softeners, pig- 'equipped with suitable means of agitation until mixture. It will be appreciated that the softness H of the coating may be varied as desired by varying the amount of softener. Preferably,'thecoat-2.

ing will be pigmented.

An artificial leather according to this invention has little tendency to exude softener upon being heated as by 'the sun in very hot weather; it surpasses in flexibility in the cold an artificial leather heretofore considered best in low temperature flexibility, namely one with a'coating consisting of pigment, nitrocellulose, and raw castor oil; and it achieves these desirable properties utilizing as softener only raw castor oil, which is-probably the cheapest softener of this art.

The manner in which these improvementsare brought about is not clearly understood. My

researches lead me to believe that the mixture of nitrocellulose with ethyl cellulose forms, with such an oil as castor oil, a gel structure which is quite difierent from the gels formed by either of the two cellulose derivatives singly with castor oil. This new, different gel structure has the rubbery resilience and freedom from stickiness desired and in'addition its'properties are much less affected by changes in temperature.

ment paste made by dispersing pigment in a portion of the softener, and solvents in a vessel a smooth dope is obtained. The solvents may be 1 similar to the usual nitrocellulose coating solvents such as, for example, a mixture of 30% ethyl acetate, 20% alcohol, and 50% toluene. However, I prefer to hold the amount of the alcohols which may :be used to between 15 and 20% by weight of the total solvent, The dope may then be, spread on the hereinbefore described flexible base, smoothed by a doctor blade, and the coat dried, preferably at an elevated temperature.

Additional coats may be applied until the desired thickness ,is obtained. The softness of the various coats may be varied. The quantity. of pigment may also be varied in the different coats. The smooth artificial leather may be embossed by the pressure of heated engraved plates or rollers .to' impart grain or other designs. I will now describe a test which I have devised to show the relative differences in flexibility at low temperaturesof various artificial leathers. This will be called the cold crack test and will be referred to in the examples to illus- "trate' further the articles in accordance with As has been indicated, I prefer in general to utilize raw castor oil as the softener of my. artificial leather and I obtain a durableproduct therewith. However, I have found that further improvement in durabilityunder the conditions of exposure to sunlight may be obtained by the utilization of an oxidized oil, slightly =polymerized, as the softener. This softener may be, for example, castor oil which has been oxidized and at the same time polymerized to such an extent -ing air at a controlled temperature.

this invention. i

A strip of artificial leather by 4 is hung in a closed chamber for 30 minutes in circulat- The strip is then picked upby the ends with gloved hands and quickly and vigorously bent 180 over a 9;! mandril rigidly'mounted in the chamber, at the same time pulling the length of the strip over the mandril,v thecoated, side being away from the mandril. The highest temperature at as to change its viscosity from the original 130 seconds Engler to 400 seconds Engler, suchas the oil known as Bakers Pale No. 4 Castor Oil. It will be appreciated that the use of highly polymerized oils reduces flexibility ini the .cold. Nevertheless, utilizing the oxidized'polymerized oil just described, a product according to this invention can be obtained which is similar in flexibility-at low temperatures to the best of the prior artand which is at the same time greatly superior in durability.

The softener utilized in the coating of my artificial leather may consist of one of the vegetable oil softeners hereinbefore mentioned,'0r a mixture of two or more thereof, or it may comprise in addition other softeners, provided that the mixture of softeners is compatible with the aforesaid cellulosic mixture used therewith. For example, it may be desired to include a resinous softener of high opacity to ultraviolet light, or a resinous softener imparting gloss, or a softener such as tricresyl phosphate and the like. When a mixture of softeners is used, the combined softener in general will be used in about the same proportion to the cellulosic mixture as hereinwlrich the coating cracks is the temperatureof failure. a I

Another test which I use to determine the quality of artificial leather measures the durability upon exposure to artificial sunlight, produced by a glass-enclosed cored-carbon arc in the device known as the Fadeometer. -A sampleis exposed until the coating reaches a condition of embrittlement such that a vigorous 180? bend over a inch mandril causes the coating to crack at each of several places tested, the coated side being away from the mandril.

- The temperature is held at about during exposure but the artificial leather is cooled for a halfhour at room temperature before a bend testis made. l v

In the examples following, the artificial leatherjin accordance with my invention is illustrated by specific examples and its properties are further described by comparison with well known art.

EXnMPLE I A coating. dope of the' composition under Formula No.1 of Table I was prepared by mixing the ingredients in a'closed vessel equipped with a slow moving agitator until a smooth dope was obtained. The pigment had previously been dispersed on a three roll mill in a portion of According to According to this in I prior art ventlon 1 i ill;

l Furumln. 1 1

Dope composition:

NlLl'll(lHlI|' Sl-'12 3 nitrogen, I50 scc owl \iscosilyuu' Ethyl cellulose-47.5% l

cthoxnhiuh viscosity. Raw castor oil l l l Oxidized castor oilllakurs lalc .\'u 4 Castor Oll 'lltlinlurn dioxide Solvent composition Ethyl acetate by weight, hutyl acetate by \\clgllt.alcoliol15C},

Lies:

. 'lcm pcrature of failure in cold crack lest. F. l5

ltliniruumtcmpcraturc causing exudation on heating lhour..'. F. Hours ul'oxpusurc in the FlldlUIllL'tUl" for cuibrittlurucnt Abowl o Ahovelllfi 100 Above 195 the softener in the ratio of 70 parts pigment to parts softener. Allcomposition figures of these examples are in parts by weight. The coating dope obtained wasthen applied to cotton broken twill cloth weighing 9 ounces per square The superior properties of this artificial leather will be readily apparent upon a comparison with an artificial leather prepared in the same manner using the composition under Formula 3 of Table I. The properties are given under the respective formulas in Table I. The two products have identical softness at room tempera-. ture, say at 70 F. and are similar in pigmentation' and in the flexible base. The article of Formula 3 has a flexibility in the cold equal to the best of prior art although its exudation temperatures is unsatisfactory in view of the requirements of the automobile industry, for example, of an exudation temperature above 175 F. to 180 F. Details of the cold crack and exposure tests have been hereinbefore discussed.

EXAMPLE II The artificial leather of this example was prepared in the same manner as that of Example I except that a coating dope of the composition under Formula 2 of Table I was used. In this example the benefits of my invention are directamples given hereinbefore are illustrative only, and in no way limiting on my invention as broadly described hereinbefore and in the appended claims.

What I claim and desire to protect by Letters Patent isz:

1-. An artificial leather consisting of a flexible base web and thereon three to fourteen ounces per square yard of coating consisting essentially of layers of, pigmented composition comprising nitrocellulose-and ethyl cellulose soluble in organic solvents, with the ethyl cellulose between 10% and 80% of. the two cellulose derivatives, and a softener essentially consisting of vegetable oil selected from the group consisting of castor oil, soya bean oil,- oxidized. castor oil, oxidized soya bean oil, oxidized cottonseed oil, partially polymerized castor oil, and mixtures thereof, said softener being compatible with the mixture of cellulose derivatives, the said composition layers being smooth, tough, homogeneous films deposited from organic solvent solutions in the absence of water and other immiscible liquids interfering with the film structure, the artificial leather being characterized by freedom from exudation of oil upon being heated, by improved flexibility at low temperatures in comparison with similar nitrocellulose artificial leather not containing ethyl cellulose, and by improved durability on exposure.

2. An artificial leather consisting of a flexible base web and thereon three to fourteen ounces per square yard of coating consisting essentially of layers of pigmented composition comprising nitrocellulose and ethyl cellulose soluble in organic solvents, with the ethyl cellulose between 10% and 80% of the two cellulose derivatives, and a softener consisting essentially of castor oil, the said composition layers being smooth, tough, homogeneous films deposited from organic solvent solutions in the absence of water and other immiscible liquids interfering with the film structure, the artificial leather being characterized by freedom from exudation of oil upon being heated, by improved flexibility at low temperatures in comparison with similar nitrocellulose artificial leather not containing ethyl cellulose,'and by improved durability on exposure.

3. An artificial leather consisting of a flexible base web and thereon three to fourteen ounces per square yard of coating consisting essentially of layers of pigmented composition comprising nitrocellulose and ethyl cellulose soluble in organic solvents, with the ethyl cellulose between 10% and 80% of the two cellulose derivatives, and a softener consisting essentially of oxidized castor oil, the said composition layers being smooth, tough, homogeneous films deposited from organic solvent solutions in the absence of water and other .immiscible liquids interfering withthe film structure, the artificial leather being characterized by freedom from exudation of oil upon being heated, by improved flexibility at low temperatures in comparison with similar nitrocellulose artificial leather not containing ethyl cellulose, and by improved durability on exposure.

4. An artificial leather consisting of a flexible base web and thereon three to fourteen ounces per square yard of coating consisting essentially of layers of pigmented composition comprising nitrocellulose andethyl cellulose soluble in organic solvents, with the" ethyl cellulose between 10% and 80% of "the two cellulose derivatives, and a softener consistingessentially of partially polymerized castor oil, the said composition layers being smooth, tough, homogeneous films nitrocellulose and ethyl cellulose soluble in organic solvents in approximately equal parts, and

deposited from organic solvent solutions in the V absence of water and other' immiscible liquids interfering with the film structure, the artificial leather being characterized by freedom from exudation of oil upon being heated, by improved flexibility at low temperaturesin comparison withsimilar nitrocellulose artificialleather not containing ethyl cellulose. and by improved durability on exposure.

a castor oil softener compatible with the said mixture of cellulose derivatives, the said composition layers being smooth, tough, homogene- 'ous films deposited from organic solvent solutions in the absence of water and other immiscible liquids interfering with the film struc: ture, the artificial leather beinacharacterized by freedom from exudation of oil upon being heated, by improved flexibility at low tempera- 5. An artificial leather consisting of a flexible 1 base 'web and thereon three to fourteen ounces per squareyard of coating consisting essentially of layers of pigmented composition comprising tures in comparison with similar nitrocellulose artificial leather not containing ethyl cellulose, and by improved durability on exposure.

- PHILIP F. ROBB." 

